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Home , Anchor escapement, Pendulum clock, Seconds pendulum

(Edited from Wikipedia)

SUMMARY

A is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a ; it swings back and forth in a precise interval dependent on its length, and resists swinging at other rates.

From its invention in 1656 by Christiaan until the 1930s, the pendulum clock was the world's most precise timekeeper, accounting for its widespread use. Throughout the 18th and 19th centuries pendulum in homes, factories, offices and railroad stations served as primary time standards for scheduling daily life, work shifts, and public transportation, and their greater accuracy allowed the faster pace of life which was necessary for the Industrial Revolution.

HISTORY

The pendulum clock was invented in 1656 by Dutch scientist , and patented the following year. Huygens contracted the construction of his clock designs to Salomon Coster, who actually built the clock. Huygens was inspired by investigations of by beginning around 1602. Galileo discovered the key property that makes pendulums useful timekeepers: isochronism, which means that the period of swing of a pendulum is approximately the same for different sized swings.

Galileo had the idea for a pendulum clock in 1637, which was partly constructed by his son in 1649, but neither lived to finish it. The introduction of the pendulum, the first harmonic oscillator used in timekeeping, increased the accuracy of clocks enormously, from about 15 minutes per to 15 per day leading to their rapid spread as existing 'verge and foliot' clocks were retrofitted with pendulums.

These early clocks, due to their verge , had wide pendulum swings of up to 100°. In his 1673 analysis of pendulums, Huygens showed that wide swings made the pendulum inaccurate, causing its period, and thus the rate of the clock, to vary with unavoidable variations in the driving force provided by the . ' realization that only pendulums with small swings of a few degrees are isochronous

1 motivated the invention of the anchor around 1670, which reduced the pendulum's swing to 4–6°.

The anchor became the standard escapement used in pendulum clocks. In addition to increased accuracy, the anchor's narrow pendulum swing allowed the clock's case to accommodate longer, slower pendulums, which needed less power and caused less wear on the movement. The , in which each swing takes one , became widely used in quality clocks. The long narrow clocks built around these pendulums, first made by William Clement around 1680, became known as grandfather clocks. The increased accuracy resulting from these developments caused the minute hand, previously rare, to be added to clock faces beginning around 1690.

The 18th and 19th century wave of horological innovation that followed the invention of the pendulum brought many improvements to pendulum clocks. The deadbeat escapement invented in 1675 by Richard Towneley and popularized by George Graham around 1715 in his precision "regulator" clocks gradually replaced the and is now used in most modern pendulum clocks.

Observation that pendulum clocks slowed down in summer brought the realization that and contraction of the pendulum rod with changes in temperature was a source of error. This was solved by the invention of temperature-compensated pendulums; the mercury pendulum by George Graham in 1721 and the gridiron pendulum by in 1726. With these improvements, by the mid-18th century precision pendulum clocks achieved accuracies of a few seconds per week.

Until the 19th century, clocks were handmade by individual craftsmen and were very expensive. The rich ornamentation of pendulum clocks of this period indicates their value as status symbols of the wealthy. The clockmakers of each country and region in Europe developed their own distinctive styles. By the 19th century, factory production of clock parts gradually made pendulum clocks affordable by middle-class families.

During the Industrial Revolution, daily life was organized around the home pendulum clock. More accurate pendulum clocks, called regulators, were installed in places of business and used to schedule work and set other clocks. The most accurate, known as astronomical regulators, were used in observatories for astronomy, surveying, and .

Beginning in the 19th century, astronomical regulators in naval observatories served as primary standards for national time distribution services. From 1909, US National Bureau of Standards (now NIST) based the US on Riefler pendulum clocks, accurate to about 10 milliseconds per day. In 1929 it switched to the Shortt-

2 Synchronome free pendulum clock before phasing in standards in the 1930s. With an error of around one second per year, the Shortt was the most accurate commercially produced pendulum clock.

Pendulum clocks remained the world standard for accurate timekeeping for 270 years, until the invention of the in 1927, and were used as time standards through World War 2. The French Time Service used pendulum clocks as part of their ensemble of standard clocks until 1954. The home pendulum clock began to be replaced as domestic timekeeper during the 1930s and 1940s by the synchronous , which kept more accurate time because it was synchronized to the of the electric power grid.

FUNCTIONALITY

All mechanical pendulum clocks have these five parts:

1. A power source; either a weight on a cord or chain that turns a pulley or sprocket, or a 2. A gear train () that steps up the speed of the power so that the pendulum can use it. 3. An escapement that gives the pendulum precisely timed impulses to keep it swinging, and which releases the gear train wheels to move forward a fixed amount at each swing. This is the source of the "ticking" sound of an operating pendulum clock. 4. The pendulum, a weight on a rod. 5. An indicator or dial that records how often the escapement has rotated and therefore how much time has passed, usually a traditional with rotating hands.

An escapement is a device in mechanical and clocks that transfers energy to the timekeeping element (the "impulse action") and allows the number of its to be counted (the "locking action"). The impulse action transfers energy to the clock's timekeeping element (the pendulum) to replace the energy lost to friction during its cycle and keep the timekeeper oscillating.

The escapement is driven by force from a suspended weight, transmitted through the timepiece's gear train. Each swing of the pendulum releases a tooth of the escapement's escape wheel gear, allowing the clock's gear train to advance or "escape" by a fixed amount. This regular periodic advancement moves the clock's hands forward at a steady rate. At the same time the tooth gives the timekeeping element a push, before another

3 tooth catches on the escapement's pallet, returning the escapement to its "locked" state. The sudden stopping of the escapement's tooth is what generates the characteristic "ticking" sound heard in operating mechanical clocks and watches.

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